Humidity is often a parameter used by engine management systems of vehicles in controlling exhaust gas recirculation (“EGR”), such as controlling an exhaust gas recirculation valve. Such engines thus typically have a humidity sensor or sensors coupled to an electronic control unit (“ECU”) of the engine management system that includes memory and software programmed therein that provides the control for the various functions of the engine management system, including control of the EGR. In particular, moisture build-up at the EGR valve can lead to icing of the EGR valve. The engine management system manages gas flow to the EGR valve to avoid icing of the EGR valve.
Since the humidity sensor impacts emissions' control, a diagnostic for the humidity sensor is included in the on-board diagnostics (“OBD”) of the vehicle's engine management system. A humidity sensor diagnostic typically requires a reference against which to compare the relative humidity sensed by the humidity sensor. Prior art approaches have addressed this such as by providing a second humidity sensor to provide the reference or to use a secondary source such as a weather station to obtain the relative humidity for an area in which the vehicle is in and communicate this data to the vehicle for use in the OBD humidity sensor output signal rationality diagnostic.